In a new post on the BioWare forums, community coordinator Chris Priestly described what players can expect from the new mode.

According to Priestly, "players can choose from a variety of classes and races, form an elite Special Forces squad, and combine their weapons, powers and abilities to devastating effect as they fight together to liberate key territories from enemy control."

Priestly also revealed that co-op missions will affect the single player campaign, having a "direct impact" and "giving players an alternative method of achieving ultimate victory."

This "alternative method" appears to be called "Mass Effect 3: Galaxy At War," a new system that will allow gamers to alter a Galactic Readiness level that gauges the player's level of preparation for the game's final battle.

Priestly wrote that "players can impact their game's Galactic Readiness level in multiple ways via the Mass Effect 3: Galaxy at War system, including multiplayer. Other platforms and interfaces will be announced in the coming months."

Most importantly, Priestly added that these cooperative modes will be completely optional, and that the full experience is still available in single-player mode.

"It is important to note that the system is entirely optional and just another way players can have control over your game experience," Priestly wrote. "It is still possible to achieve the optimal, complete ending of the game in Mass Effect 3 through single-player alone."

Priestly confirmed that the game's multiplayer will be limited to cooperative play and will not include competitive multiplayer. He added that the co-op modes were developed by a team that was completely separate from those who developed the single-player campaign.

Finally, it was revealed that co-op will not feature existing characters, and that instead "players will create custom characters to fight on different and unique fronts in the war. This will include the ability to play as favorites like Turians, Krogans, Asari and more…each with their own unique set of abilities." These characters will level up and be able to upgrade weapons during the course of co-op play.

Mass Effect 3 is set to hit stores on March 6, 2012. For our full thoughts on the introduction of cooperative multiplayer, check out our multiplayer reactions from earlier today.